1. Field of the Invention
The invention relates generally to the field of lithography systems and, more particularly, to management of reaction loads in a lithography tool.
2. Background Art
In the fabrication of integrated circuits, lithographic and projection printing techniques are used. Lithography is a process used to create features on the surface of substrates. Such substrates can include those used in the manufacture of flat panel displays, circuit boards, various integrated circuits, and the like. A frequently used substrate for such applications is a semiconductor wafer. During lithography, exposure optics located within a lithography apparatus project an image in a reticle onto the surface of a semiconductor wafer. The wafer is disposed on a wafer stage. The projected image produces changes in the characteristics of a layer of the wafer. For instance, a photoresist layer deposited on the surface of the wafer is etched with a pattern during the process.
Step-and-scan lithography techniques may be used to expose a wafer. Rather than expose the entire wafer at one time, individual fields are scanned onto the wafer, one at a time. This is done by moving the wafer and reticle simultaneously such that an imaging slot is moved across each field during the scan. The wafer stage is stepped between field exposures to allow multiple copies of the reticle pattern to be exposed over the wafer surface.
As a result, components are required to move in step-and-scan lithography systems. Acceleration of system components during their movement can cause a reaction load or reaction movement in components of the system being moved against, and in the support structure. Reaction movements or reaction loads lead to relative motion between critical components, and possible shaking of the support structure, which leads to reduced operational precision for the lithography system. Hence, what is needed is a method, system, and apparatus for reducing reaction loads, support structure shaking, and relative motion among lithography system components.
A lithography apparatus that incorporates an isolation system with a reaction load management mechanism, and a method for assembling the same is described herein. The lithography apparatus includes an isolated structure, a moveable stage, a linear motor, a flexure mechanism, and a flexure rod. The isolated structure is supported by a non-isolated structure. The isolated structure supports the moveable stage. The linear motor includes a first linear motor element and a second linear motor element. The first linear motor element is coupled to the moveable stage. The second linear motor element is mounted on the isolated structure by a flexure mechanism. The flexure mechanism preferably includes a plurality of parallel flexure plates. The flexure rod is coupled between the non-isolated structure and the second linear motor element.
The parallel flexure plates form a parallel flexure mechanism that allows movement in a first linear degree of movement, parallel to the axis of motion of the stage. In further embodiments, a flexure rod coupled between the non-isolated structure and the second linear motor element accommodates the remaining two linear and three rotational degrees of freedom.
The combination of the flexure rod and parallel flexure mechanism provides a high degree of compliance in all six degrees of freedom, thus preventing vibration from being coupled from the non-isolated structure to the isolated structure. The isolated structure remains free to move with respect to non-isolated structure.
The passive flexured mechanism of the present invention directly transfers motion related loads from the second element of the linear motor to the non-isolated support structure. This transfer is accomplished without dissipating substantial power, or compromising the isolation of the structure on which the stage is mounted. By reducing the motion loads, and hence reducing the shaking of lithography system components, semiconductor wafers may be more precisely and repeatedly etched according to tighter tolerances.
The present invention reduces reaction loads related to an isolated stage mechanism that is moveable along a single axis, along two axes, and along additional axes.